This invention relates to frontlit electronic displays.
Flat panel displays are typically backlit by light guide slabs (often referred to as xe2x80x9cbacklightsxe2x80x9d) that provide uniform illumination to a transmissive light valve. The backlight may be the primary light source for the display, or a source of supplemental illumination in a predominantly reflective (often referred to as a xe2x80x9ctransflectivexe2x80x9d) display. Alternatively, flat panel reflective displays may be front-lit by a light guide slab (often referred to as a xe2x80x9cfrontlightxe2x80x9d or xe2x80x9cfront light guidexe2x80x9d) that provides uniform illumination from the viewing side of a reflective light valve. This allows elimination of the backlight and placement of a reflective layer in the light valve, thereby increasing the display""s reflectivity and brightness in well-lit ambient light conditions when the frontlight is turned off. Front light guides should have sufficient clarity so that they do not distort or significantly attenuate the display image. Preferably the front light guide also uniformly illuminates the display at a brightness level sufficient to render the display readable in dark ambient conditions.
U.S. Pat. No. 5,396,350 shows a backlight having an array of microprisms that reflect light into a transmissive light valve.
U.S. Pat. No. 5,428,468 shows an illumination system employing a waveguide and an array of microprisms that reflect light out of the waveguide. U.S. Pat. No. 5,995,690 shows a light extraction tape for coupling light out of a waveguide.
Japanese Published Patent Application No. JP 11344695A (equivalent to WO 9963394) shows an integral front light guide and touch panel in which the light guide portion is made of molded plastic. The upper surface of the light guide is bonded to the lower surface of the touch panel using a layer of transparent resin, and the lower surface of the light guide has a polygonal or circular dot pattern formed by an ink of transparent or semi-transparent resin having a higher refractive index than the light transmission plate and containing a photodiffusion pigment. Alternatively, the lower surface of the light guide can be formed with xe2x80x9cfine crimpsxe2x80x9d or with xe2x80x9cprismsxe2x80x9d (shown as sawtooth projections) formed parallel to the end face of the input of the light transmission plate. The light guide of this reference utilizes scattering by the above-mentioned photodiffusion pigment, or refraction through the above-mentioned crimps or prisms, to extract light from the light guide into a light valve. The sawtooth projections in this reference are oriented with the inclined portion of the sawtooth facing away from the light input end of the light guide.
Japanese Published Patent Application No. JP 2000-47178A shows an integral front light guide and touch panel in which the light guide portion is wedge-shaped and has a pattern of spacers on its upper surface. The light guide of this reference utilizes scattering by the spacers to extract light from the light guide into a light valve.
Other illuminated frontlit or backlit illumination or display devices are shown in U.S. Pat. Nos. 4,373,282; 4,528,617; 4,751,615; 4,799,137; 4,811,507; 4,874,228; 5,005,108; 5,050,946; 5,054,885; 5,190,370; 5,341,231; 5,359,691; 5,485,354; 5,506,929; 5,555,109; 5,555,329; 5,575,549; 5,594,830; 5,608,550; 5,608,837; 5,613,751; 5,668,913; 5,671,994; 5,835,661; 5,894,539; 6,011,602 and 6,139,163; in European Patent Application EP 0 802 446 A1; in Japanese Published Patent Application Nos. JP 61188515A, JP 11065764A, JP 11110131A, JP 11174972A, JP 11260133A, JP 11316553A, JP 11065764A and JP 2000075293A; and in PCT Published Patent Application No. WO 99/63394A.
Although a number of illuminated display devices have been proposed, there is an ongoing need for thinner, more efficient or more evenly illuminated devices, for devices that could be more easily constructed, and for devices with reduced power consumption. Many current devices do not use all of the light supplied by the light source. If such unused light could be channeled to the display, then power consumption could be further reduced and display brightness could be increased.
Some of the above-mentioned illuminated display devices employ scattering or refraction to extract light from the light guide. These approaches can cause reduction in contrast, or can supply light at less than optimal angles to a light valve in the display.
The present invention provides, in one aspect, an illuminated display comprising:
a) at least one light source;
b) a front light guide having at least one light input face through which light from the source can be supplied to the guide, a viewing face, and a light output face opposite the viewing face, the light output face having a light extraction layer thereon, the extraction layer having a substantially flat light exit face and containing buried reflective facets that extract supplied light from the guide through the light exit face; and
c) a reflective light valve that receives extracted light from the guide and returns at least some of that light through the viewing face.
The light guide can be easily fabricated from, for example, molded plastic or glass (e.g., ordinary plate glass) having two major faces. One of the major faces forms the viewing face, and is used as is or provided with an optional protective overlayer. The other major face forms the light output face, and is adhesively bonded or otherwise fastened to the structured side of a structured-surface, smooth surface sheet. The structured surface has facets on the structured side that will reflect supplied light from the light output face of the light guide through the smooth surface (the light exit face) of the sheet and into the reflective light valve. An optional antireflection coating can be applied to the light exit face of the smooth surface sheet. Because the light guide has microstructured reflective optics located between the light guide and the light valve and because the light guide can have a smooth viewing face, the illuminated displays of the invention are relatively robust and are less likely to be damaged than illuminated displays having microstructured optical features on the viewing face of a light guide. Preferred embodiments of the displays of the invention efficiently extract supplied light while exhibiting good contrast and low distortion.